<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <input type="button" value="添加" id="btn">

    
</body>
<script>
    var btn = document.getElementById('btn');
    btn.onclick=function(){
        alert('确定');
    }
    btn.onclick = null;
</script>
</html>